Conventionally, an inertia force sensor having a device layer, an upper substrate and a lower substrate is proposed in, for example, JP-A-2004-333133. The device layer includes a movable portion and the like. The upper substrate is bonded to the upper side of the device layer, and the lower substrate is bonded to the lower side of the device layer. Thus, the movable portion in the device layer is sealed with the upper and lower substrates. The upper substrate functions as a cap layer for covering the movable portion so that the upper substrate prevents water and foreign particle from penetrating into the movable portion.
Further, the upper substrate includes a through hole so as to expose a part of the device layer. Thus, a pad on the device layer is exposed in the through hole. A bonding wire is connected to the pad via the through hole so that the device layer is coupled with an external system electrically.
In the prior art, the through hole having a large depth is formed in the cap layer, and the bonding wire is connected to the device layer in a bottom of the through hole. Alternatively, the present inventors have proposed a structure of a sensor layer and a cap layer directly bonded together in Japanese Patent Application No. 2008-4144. Specifically, in the structure, a movable portion is formed in the sensor layer via a wiring patter, and the sensor layer and the cap layer are integrated.
However, it is necessary to flatten a surface of the wiring pattern since a flat surface of the sensor layer and a flat surface of the cap layer are bonded together. Further, even when the surface of the wiring pattern is flattened, a foreign particle may attach the surface of the wiring pattern. In such a case, the surface of the wiring pattern is roughened, and thereby, the sensor layer and the cap layer are not directly bonded together. Thus, connection and conduction in the device may be damaged.
Further, conventionally, a semiconductor physical quantity sensor for detecting physical quantity such as acceleration, yaw rate and vibration is disclosed in JP-A-H09-129898, JP-A-H11-295336, and JP-A-H06-123628. The sensor detects the physical quantity by detection of capacitance change between a movable portion and a fixed portion. The movable portion has a beam structure. The movable portion and the fixed portion are formed in a multi-layered SOI substrate, and function as a sensing portion. A wiring for connecting between parts of the sensor is made of poly crystal silicon.
Further, in JP-A-2004-333133, the cap layer covers the movable portion so that water and/or foreign particle are prevented from penetrating into the movable portion. The cap layer includes multiple through holes, and a bonding wire is directly bonded to a wire bonding pad of the SOI substrate. Thus, the bonding wire functions as a wiring layer.
Further, a semiconductor physical quantity sensor is disclosed in JP-A-2004-311951. In the sensor, a movable portion and the like is formed in a silicon layer of a SOI substrate, and a signal processing circuit is formed in a silicon layer of another SOI substrate. The silicon layer of the SOI substrate is bonded to the other silicon layer of the other SOI substrate via a ring shape bump. Another example of the ring shape bump is disclosed in JP-A-H11-94506. In these sensors, a wiring layer is formed in the sensor so as to electrically couple between the signal processing circuit and an external circuit. Further, the wiring layer is insulated from the ring shape bump, and the wiring layer steps over the bump, and the wiring layer is retrieved to the outside of the ring shape bump.
However, in the techniques disclosed in JP-A-H09-129898, JP-A-H11-295336, and JP-A-H06-123628, since the wiring layer made of poly crystal silicon is formed on the same substrate, on which the sensing portion is formed, a manufacturing process is complicated, and a manufacturing yield of the sensor is reduced.
Further, in the technique disclosed in JP-A-2004-333133, it is necessary to form multiple through holes ion the cap layer. Further, since the bonding wire is bonded to the wire bonding pad with using a bonding tool, it is necessary to form the through hole having a sufficient diameter so as not to contact the tool on an inner wall of the through hole. Thus, a chip size of a semiconductor chip, on which the semiconductor physical quantity sensor is formed, increases.
In the technique of JP-A-2004-311951, since the wiring layer steps over the ring shape bump, it is necessary to insulate the bump and the wiring layer with using an insulation film between the bump and the wiring layer. Thus, a structure of the semiconductor physical quantity sensor is complicated.